1. Field of the Invention
This invention relates to fluid control valves, and more particularly, to an annular valve seat for use in both normal and relatively high temperature environments.
2. Description of the Prior Art
Butterfly and other types of fluid control valves with annular resilient seals are well known and commonly used for controlling the flow of various fluids at ambient or moderate temperatures and modest pressures in a wide variety of industries. Such control valves commonly have a generally annular body defining a fluid flow passage having a valve seat around the flow passage and a metallic flow control disc movably supported in the flow passage for controlling the flow of fluids through the valve. The valve is closed by pressing the disc against the valve seat to prevent the flow of fluid through the valve. Valves used at moderate temperatures and modest pressures commonly use annular resilient seals in the valve seat while metal seals are used at higher temperatures and higher pressures. Such metallic seals usually permit more leakage of fluid than do the resilient seals if used at lower temperatures. For this reason when the normal operating temperature is relatively low resilient seals are commonly used. However, in the petroleum industry there is sometimes the danger of a fire either inside the piping system itself or outside the piping system in the vicinity of the valve. When fire causes the valve temperature to rise to higher levels, the resilient seal of the valve can deteriorate or be destroyed so that it will no longer be effective as a seal.
Some of the prior art valves use a resilient seal when the valve is operating at a lower temperature and have a backup metal seal which moves into operating contact with a valve disc when the resilient seal is damaged. Such a backup valve seat may operate satisfactorily when the resilient seal is completely destroyed, but may have excessive fluid leakage when a portion of the resilient seal remains in the fluid flow passage.
What is desired is a fluid-control valve having both a resilient valve seal and a metal seat that maintain fluid-tight contact with the flow control disc when moderate temperatures are present in the valve, and wherein the metal seat continues to maintain said fluid-tight contact if the resilient seal is partially or completely destroyed.